Photocell controlled pattern tracer

ABSTRACT

A friction drive and steering mechanism for a pattern tracing machine, such mechanism including a drive wheel frictionally engaging a drive surface and steerable about an axis intersecting the drive surface at a point displaced from the point of engagement of the drive wheel with the surface, and a photooptical tracing head arranged to view an area on the drive surface close to said steering axis and means for steering the viewed area about the steering axis in such a manner that a line is maintained between a point in the viewing area and the axis parallel to a tangent to the pattern in the viewing area.

O United States Patent [151 ,660,665

Luker [451 May 2,1972

[ 54 PHOTOCELL CONTROLLED PATTERN 3,514,862 6/ 1970 Helgemeir ..250/202 X TRACER 3,497,694 2/1970 Jura et al. 250/202 3,496,437 2/1970 Layden ..250/202 X [72] Inventor: Ronald J. Luker, Hamilton, Ontario,

Canada Primary Examiner-Archie R. Borchelt [73] Assignee: Westlnghouse Canada Limited A'mmey -R' Fox [22] Filed: May 5, 1970 [57] ABSTRACT [21 A NQ 34,72] A friction drive and steering mechanism for a pattern tracing machine, such mechanism including a drive wheel frictionally engaging a drive surface and steerable about an axis intersect- [30] Forelgn Application Priomy Data ing the drive surface at a point displaced from the point of en- July 13, 1969 Canada ..055,983 gagemem of the drive wheel with the Surfaceand a P P tical tracing head arranged to view an area on the drive sur- [52] U.S.Cl ..250/202 face close to Said Steering Taxis and means for Steering the 5 Int CL os 1/01 viewed area about the steering axis in such a manner that a 58] Field f Search I 250/202 line is maintained between a point in the viewing area and the axis parallel to a tangent to the pattern in the viewing area. [56] References Cited 4 Claims, 7 Drawing Figures UNITED STATES PATENTS 3,385,122 5/1968 Jewell ..250/202 X PATENTEDMAY 2 I972 SHEET 1 OF 3 F I61 (Prior Art) FIG. 2

AMPl lF/ER Can/mot 5 9 PI-IOTOCELL CONTROLLED PATTERN TRACER This invention relates to pattern cutting machines primarily of the type utilizing cutting torches for producing shaped patterns from metal sheet in accordance with an optical pattern.

It has been common practice to mount one or more gas cutting torches on a machine in such a manner that movement of the machine will cause the torch to execute a determined pattern and thus cut a suitably shaped piece from the metal placed in proper relationship to the torch. Typical of such machines are those which are mounted on a pair of slides or tracks and are usually referred to as co-ordinate drive machines and also machines referred to as pantographic machines" where the torches are mounted on articulated arms.

In order to control the shape of the piece cut from the sheet material, it has been common practice in the past to control the motion of the torch in accordance with a predetermined pattern. This pattern may consist of a physical pattern'followed by-a mechanical tracer,a magnetic pattern followed by a magnetic follower or as in the present case an optical pattern followed by an optical pattern following apparatus. One of the common methods of driving the mechanism is to cause a friction drive wheel to engage a surface parallel to the surface of the pattern to be traced and to the surface of the material to be cut, drive the wheel at a constant velocity determined by the cutting capability of the cutting apparatus-and steer the wheel at the same time in accordance with the desired pattern. If the wheel is maintained tangential to the edge of the pattern by means of some pattern following apparatus and is driven at constant velocity then the wheel will trace out a path corresponding to the desired pattern.

Early methods of obtaining this end were to steer the wheel manually around the edge of the pattern. If the torch is now mechanically coupled to the wheel so that it executes the same path as the wheel, it may be caused to cut the material into a pattern in a shape identical to the pattern.

Improvements to such equipment substituted electro-opti cal devices for the human eye. The pattern was viewed by such an electro-optical device, which maintained itself in a fixed tangential relationship to the pattern. The angular direction of the optical device was then used to steer the drive wheel. In order that the electro-optical device remain over the pattern, it will then be seen to be necessary that a line joining the steering axis of the drive wheel and the steering axis of the electrooptical device remain parallel to a reference line in the pattern.

This concept will become more apparent when one considers for example, a co-ordinate drive machine which consists of a carriage mounted for motion in a single direction, for example, in the X direction on a bridge which is in turn mounted for motion in a further direction at right angles thereto, for example, the Y direction. If the electro-optical tracer, which is to be maintained tangential to the pattern, and the friction drive wheel, which is to provide direction and velocity to the carriage, are both mounted on the carriage and coupled together so as to maintain the same tangential direction the convolutions of the path of the drive wheel will be repeated by the electro-optical viewing device and the device will thereby be kept over the pattern.

Machines of the foregoing type are all well known and in common use. There is however a further type of machine, generally referred to as a broken-arm machine, which consists of a simple articulated arm at the end of which is mounted a cutting torch. Efforts to use this type of machine for pattern tracing have been limited to simple situations where the pattern is arranged above the torch and the drive wheel is coincident axially with the torch. Manual pattern tracers have been provided in the past for this type of machine but automatic optical followers have not been available.

A clearer understanding of the specific prior art referred to herein and my invention will be had from the following description and drawings in which:

FIG. I is a plan view ofa broken-arm machine, in schematic only, of the type referred to as the prior art;

FIG. 2 is a sectional view of the apparatus of FIG. 1; along section line 2-2;

FIG. 3 is a plan view of a machine in accordance with my invention;

FIG. 4 is a section of the apparatus of FIG. 3 along section line 4-4;

FIG. 5 is an electro-optical tracing head and drive mechanism in accordance with myinvention;

FIG. 6 is a fragment in section of the portion of the apparatus of FIG. 5; and

FIG. 7 is a block schematic diagram of the associated electrical circuitry.

Considering first FIGS. 1 and 2, it will be seen that in these figures there is illustrated, very schematically, a broken-arm machine which consists of two beams 8 and 9 pivoted at pivot 10 and mounted for rotation on shaft 11. At the end of arm 9 is mounted a gas cutting torch l2 and directly above torch 12 and coaxial therewith is a tracing point 13. The material to be cut such as a metal sheet 14 is suitably supported on bed 15 and the pattern to be traced is supported on the lower surface of table 16. Tracing point 13 may now be moved around the pattern manually, by observation or by some other means and if the torch 12 is operating an article will be cut from sheet 14 in'a shape determined by the pattern on the table 16. If the tracing point 13 is now replaced by a driven friction wheel, it is possible, by steering the friction wheel, to cause it to follow the pattern. However, as will be seen, it is not practical to optically view the pattern at the same point as the point of engagement of the friction drive wheel. Therefore the wheel would have to be placed to one side of the optical viewing point. However, as has been indicated, in a machine of this type, in order that the optical viewing device shall maintain its position relative to the pattern to be traced, it is necessary that the torch, the steering axis of the drive wheel, and the optical viewing point all effectively follow the same path and a line joining the steering axis of the optical viewing device and the steering axis of the drive wheel must be maintained parallel to a fixed line. It also will be noted that the pattern is on the under side of the table which is a substantial disadvantage.

In FIG. 3 there is shown a broken-arm machine in accordance with my invention. Here again the machine consists of a pair of beams 17 and 18 pivoted at a point 19 and mounted for rotation around the shaft 20. The arm 18, however, consists of a U-shaped member as is more clearly seen in FIG. 4. The upper leg 21 supports an electro-optical pattern I tracing device 22 and a lower legs 23 supports the cutting torch 24. A table 25 supports the pattern to be followed and a bed 26 supports a sheet of material to be cut 27. The bed 26 may also provide the support for 7 column 28 on which is mounted the shaft 20.

Turning now to FIG. 5, there will be seen in greater detail elements of the electro-optical tracer drive 22. The friction drive wheel referred to previously has designation 29 and is driven by virtue of its being rigidly mounted on shaft 30, which in turn is connected to wheel 31. Wheel 31 frictionally engages the face of a gear 32 which gear is driven by pinion 33 on the shaft of motor 34. The gear 32 is mounted for rotation in the body or housing of the apparatus 35 by means of an extended quill 36, which is retained in bearings 37 and 38, mounted in the body 35. A photo-optical viewing device 39 is mounted between wheels 29 and 31 and consists of a block 40 more clearly seen in FIG. 6 in which is mounted a pair of photocells 41 and 42. Also mounted on the block 40 is a lamp 43. The whole block 40, together with the photocells and the lamp is mounted for transverse adjustment by means of a threaded shaft 44 which is manually rotatable by means of a knurled nut 45, which is axially fixed but free to rotate in the steerable assembly 46. This steerable assembly in turn is rotatably mounted within the quill 36 by means of a hollow shaft 47. The shaft is hollow to accommodate the necessary electrical conductors from the photo-optical tracing head which are carried up through the center of the hollow shaft and connect to various slip rings 48, 49, 50 etc., mounted on an insulator at the top end of shaft 47. By means of brushes 51, 52, 53 etc., connections can be made from the photo-optical tracer to other components in the system. The upper end of shaft 47 is connected to motor 54 by means of a coupling 55.

Turning now to FIG. 7, it will be seen that the output from the photocells 41, 42 are applied to a signal converter 56 which changes the photocell signal into a signal useful to the amplifier 57 which in turn applies its output to the reversible motor 54. A suitable source of supply is applied to terminal 58 for example, 110 volts, 60 cycles and this power is applied through control 59 to the amplifier 57 and to the drive motor 34. This diagram is shown in single line form. It will be understood that each connecting line may represent a plurality of conductors and include devices such as slip rings 48 and brushes 51.

OPERATION Let us assume that the apparatus is arranged as shown in FlGS, 3 and 4 with a suitable pattern on surface and a suitable power supply applied to 58. Lamp 43 will illuminate the pattern on surface 25. The light from the lamp 43 will be reflected back into the photocells 41 and 42 and the amount of light reflected back will be determined by the nature and position of the pattern viewed by the two photocells. Assuming that the areas of the two photocells 41 and 42 are not completely coincident and assuming that pattern consists of a line having a different coefficient of reflectivity than the surface on which it is drawn and is somewhere within the pattern of view of at least one of the photocells, then the output from the two photocells will differ if the pattern is not located equally within the fields of view of both photocells. Assuming such condition to exist and the two photocells to have unequal outputs, then when the outputs from the photocells 41 and 42 are applied to the signal converter 56 it produces a signal of one characteristic if the photocell 42 is more exposed tothe pattern than photocell 41 and of a different characteristic if photocell 41 is more exposed to the pattern then photocell 42. These signals of opposite character, for example, opposite polarity, are applied to amplifier 57 and create an output, which when applied to motor 54, causes the motor to rotate in one direction or the other depending upon the characteristic of the signal applied to the amplifier and with a speed dependent upon the difference between the signals produced by photocells 41 and 42. Hence the motor 54 will rotate with a speed and direction which is a function of the degree of overlap of the field of view of photocell 41 and the pattern as compared to the degree of overlap of the field of view of photocell 42 and the pattern. As will be seen the motor 54 is mechanically coupled to the mechanism 46 which steers the drive wheel 29 and, if all components are properly oriented, causes the drive wheel 29 to be maintained parallel to a line tangential to the pattern.

The exact mode of operation of this portion of the system will not be explained because photo-optical tracers of this type are known in the art using one or more photocells and associated circuitry and equipment. It is only necessary that the photo sensitive area be effectively located between the wheels 29 and 31 and substantially on the axis of steering of the wheels. This may be accomplished for example by physically locating the photocells in such location or by optically coupling them through fiber optical devices to such location. The wheels are steered by motor 54, and are driven by motor 34. The electrical supply from terminal 58 is applied through control 59 to the motor 34. The control 59 permits an operator to regulate the speed of rotation of motor 34 and may permit signals from the signal converter to also control either the speed of motor 34 or its operation. When motor 34 rotates it drives pinion 33 which in turn drives gear 32. Since wheel 31 frictionally engages the surface of gear 32, rotation of motor 34 drives the wheel 31 which in turn drives the wheel 29. Wheel 29 in turn engages the surface of 25 on which the pattern is laid. As was previously indicated, the wheel is steered by motor 54 and maintained tangential to the pattern. It is now driven at a velocity determined by motor 34 it will cause the tracing head 22 to progress across the surface 25 in a direction determined by the pattern and with a constant velocity determined by the speed of motor 34. It will be noticed that the drive wheel 29 is offset from the steering axis and that the photo-optical devices are also slightly offset from the steering axis. The reason for both these offsets will be understood by those familiar with the art. An explanation of both these factors is provided, for example, in Canadian Pat. application No. 772,895.

As will be appreciated, with the steering axis of both the photocells and the driving wheels being coincident, the requirement that a line joining these two axes remain parallel to a reference line ceases to be a problem and there is no need for pantographic or parallel axis operation. As the steering motor rotates the photocells, it similarly rotates the drive wheel and the tracing head 22 traces the pattern at a velocity determined by the speed of rotation of the drive wheels. At the same time, because the upper arm 21 is rigidly coupled to the lower arm 23, the torch 24 follows the same convolutions as the tracing head 22. In this way, when operative, the torch will cut from material 27 a piece shaped in accordance with the shape of the pattern on surface 25.

While the foregoing description has been directed to a specific form of the device having a preferred embodiment, it will be understood that the coincidence of steering axes of the drive wheel and the photo-optical tracing head is the essential aspect of the invention. Various modes of operation of the tracing head and arrangement of the head and torches may be provided within the scope of this invention, but it will always be necessary that the axes, as referred to, be coincident. It will also be understood that in order for such axes to be coincident, the point of contact of the drive wheel 29 cannot be coincident with the steering axis and it must therefore be displaced to one side in the manner shown.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pattern tracing machine including a friction drive wheel rotatable about a drive axis parallel to a drive surface and steerable about a steering axis perpendicular to said drive surface and a photo-optical tracing head arranged to view a pattern on said drive surface and maintain said drive axis perpendicular to a tangent to that portion of the pattern viewed by said tracing head and the steering axis intersecting the pattern, wherein the point of contact of the drive wheel and the drive surface is close to the point of intersection of the steering axis and the drive surface, but displaced along a line parallel to said drive axis and wherein said tracing head is mounted for rotation about said steering axis with the portion of the pattern viewed by said tracing head lying on said tangent and almost coincident with the point of intersection of the steering axis and the pattern.

2. A pattern tracing machine as claimed in claim 1 wherein the displacement of the point of driving engagement of said wheel from said intersection point is such as to compensate for velocity variations which would otherwise be introduced into the system by steering.

3. A pattern tracing machine as claimed in claim 1 wherein said friction drive wheel and said photo sensitive device are mounted for rotation about said steering axis by a common steering motor.

4. A pattern tracing machine as claimed in claim 3 wherein said steering motor is energized in accordance with the illu mination received by said photo sensitive device. 

1. A pattern tracing machine including a friction drive wheel rotatable about a drive axis parallel to a drive surface and steerable about a steering axis perpendicular to said drive surface and a photo-optical tracing head arranged to view a pattern on said drive surface and maintain said drive axis perpendicular to a tangent to that portion of the pattern viewed by said tracing head and the steering axis intersecting the pattern, wherein the point of contact of the drive wheel and the drive surface is close to the point of intersection of the steering axis and the drive surface, but displaced along a line parallel to said drive axis and wherein said tracing head is mounted for rotation about said steering axis with the portion of the pattern viewed by said tracing head lying on said tangent and almost coincident with the point of intersection of the steering axis and the pattern.
 2. A pattern tracing machine as claimed in claim 1 wherein the displacement of the point of driving engagement of said wheel from said intersection point is such as to compensate for velocity variations which would otherwise be introduced into the system by steering.
 3. A pattern tracing machine as claimed in claim 1 wherein said friction drive wheel and said photo sensitive device are mounted for rotation about said steering axis by a common steering motor.
 4. A pattern tracing machine as claimed in claim 3 wherein said steering motor is energized in accordance with the illumination received by said photo sensitive device. 